Merge pull request #3477 from densh/topic/syntactic-empty-type-tree

Rename EmptyTypTree into SyntacticEmptyTypeTree

4 files changed, 23 insertions, 11 deletions

diff --git a/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala b/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
index 0c73214745..2eb50d5993 100644
--- a/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
+++ b/src/compiler/scala/tools/reflect/quasiquotes/Reifiers.scala
@@ -190,6 +190,8 @@ trait Reifiers { self: Quasiquotes =>
         reifyBuildCall(nme.SyntacticFunction, args, body)
       case SyntacticIdent(name, isBackquoted) =>
         reifyBuildCall(nme.SyntacticIdent, name, isBackquoted)
+      case SyntacticEmptyTypeTree() =>
+        reifyBuildCall(nme.SyntacticEmptyTypeTree)
       case Q(Placeholder(Hole(tree, DotDot))) =>
         mirrorBuildCall(nme.SyntacticBlock, tree)
       case Q(other) =>
diff --git a/src/reflect/scala/reflect/api/BuildUtils.scala b/src/reflect/scala/reflect/api/BuildUtils.scala
index 3bcf751ace..7aaa3973b3 100644
--- a/src/reflect/scala/reflect/api/BuildUtils.scala
+++ b/src/reflect/scala/reflect/api/BuildUtils.scala
@@ -248,6 +248,13 @@ private[reflect] trait BuildUtils { self: Universe =>
       def unapply(tree: Tree): Option[(Tree)]
     }
 
+    val SyntacticEmptyTypeTree: SyntacticEmptyTypeTreeExtractor
+
+    trait SyntacticEmptyTypeTreeExtractor {
+      def apply(): TypeTree
+      def unapply(tt: TypeTree): Boolean
+    }
+
     val SyntacticFor: SyntacticForExtractor
     val SyntacticForYield: SyntacticForExtractor
 
diff --git a/src/reflect/scala/reflect/internal/BuildUtils.scala b/src/reflect/scala/reflect/internal/BuildUtils.scala
index 6106339324..458c10e69b 100644
--- a/src/reflect/scala/reflect/internal/BuildUtils.scala
+++ b/src/reflect/scala/reflect/internal/BuildUtils.scala
@@ -537,13 +537,15 @@ trait BuildUtils { self: SymbolTable =>
       def unapply(tree: Tree): Option[Tree] = gen.Filter.unapply(tree)
     }
 
-    // abstract over possible alternative representations of no type in valdef
-    protected object EmptyTypTree {
-      def unapply(tree: Tree): Boolean = tree match {
-        case EmptyTree => true
-        case tt: TypeTree if (tt.original == null || tt.original.isEmpty) => true
-        case _ => false
-      }
+    // If a tree in type position isn't provided by the user (e.g. `tpt` fields of
+    // `ValDef` and `DefDef`, function params etc), then it's going to be parsed as
+    // TypeTree with empty original and empty tpe. This extractor matches such trees
+    // so that one can write q"val x = 2" to match typecheck(q"val x = 2"). Note that
+    // TypeTree() is the only possible representation for empty trees in type positions.
+    // We used to sometimes receive EmptyTree in such cases, but not anymore.
+    object SyntacticEmptyTypeTree extends SyntacticEmptyTypeTreeExtractor {
+      def apply(): TypeTree = self.TypeTree()
+      def unapply(tt: TypeTree): Boolean = tt.original == null || tt.original.isEmpty
     }
 
     // match a sequence of desugared `val $pat = $value`
@@ -561,8 +563,8 @@ trait BuildUtils { self: SymbolTable =>
         case ValDef(_, name1, _, Match(MaybeUnchecked(value), CaseDef(pat, EmptyTree, Ident(name2)) :: Nil)) :: UnPatSeq(rest)
           if name1 == name2 =>
           Some((pat, value) :: rest)
-        // case q"${_} val $name: ${EmptyTypTree()} = $value" :: UnPatSeq(rest) =>
-        case ValDef(_, name, EmptyTypTree(), value) :: UnPatSeq(rest) =>
+        // case q"${_} val $name: ${SyntacticEmptyTypeTree()} = $value" :: UnPatSeq(rest) =>
+        case ValDef(_, name, SyntacticEmptyTypeTree(), value) :: UnPatSeq(rest) =>
           Some((Bind(name, self.Ident(nme.WILDCARD)), value) :: rest)
         // case q"${_} val $name: $tpt = $value" :: UnPatSeq(rest) =>
         case ValDef(_, name, tpt, value) :: UnPatSeq(rest) =>
@@ -604,8 +606,8 @@ trait BuildUtils { self: SymbolTable =>
       def unapply(tree: Tree): Option[(Tree, Tree)] = tree match {
         case Function(ValDef(Modifiers(PARAM, _, _), name, tpt, EmptyTree) :: Nil, body) =>
           tpt match {
-            case EmptyTypTree() => Some((Bind(name, self.Ident(nme.WILDCARD)), body))
-            case _              => Some((Bind(name, Typed(self.Ident(nme.WILDCARD), tpt)), body))
+            case SyntacticEmptyTypeTree() => Some((Bind(name, self.Ident(nme.WILDCARD)), body))
+            case _                        => Some((Bind(name, Typed(self.Ident(nme.WILDCARD), tpt)), body))
           }
         case UnVisitor(_, CaseDef(pat, EmptyTree, body) :: Nil) =>
           Some((pat, body))
diff --git a/src/reflect/scala/reflect/internal/StdNames.scala b/src/reflect/scala/reflect/internal/StdNames.scala
index 53475be479..7c979e7bdc 100644
--- a/src/reflect/scala/reflect/internal/StdNames.scala
+++ b/src/reflect/scala/reflect/internal/StdNames.scala
@@ -602,6 +602,7 @@ trait StdNames {
     val SyntacticBlock: NameType       = "SyntacticBlock"
     val SyntacticClassDef: NameType    = "SyntacticClassDef"
     val SyntacticDefDef: NameType      = "SyntacticDefDef"
+    val SyntacticEmptyTypeTree: NameType = "SyntacticEmptyTypeTree"
     val SyntacticFilter: NameType      = "SyntacticFilter"
     val SyntacticFor: NameType         = "SyntacticFor"
     val SyntacticForYield: NameType    = "SyntacticForYield"